It is a screen shot of a screen shot that has made gallery throw a wobbly. You get the picture you opened in gallery "behind" your icons and widgets that follows you through swiping through home screens. A bug, but a reboot cures it. Just done it myself here you go :

It is a screen shot of a screen shot that has made gallery throw a wobbly. You get the picture you opened in gallery "behind" your icons and widgets that follows you through swiping through home screens. A bug, but a reboot cures it. Just done it myself here you go :